1. Field of the Invention
The present invention relates to a digital camera that captures object light and generates an image signal.
2. Description of the Related Art
In recent years, besides conventional cameras which take pictures using silver films, there have rapidly become widespread digital cameras using a solid-state image pickup device, such as a CCD image pickup device or MOS image pickup device, which form an object image on the solid-state image pickup device and generate an image signal.
The digital camera, which is also required to have high portability as well as high picture-taking performance, is designed so that the taking lens can be retracted into the thin body to vary the focal length and take a picture with a desired angle of view and for the convenience of carriage.
As the taking lens having a variable focal length, a taking lens composed of three or more lens groups is used. Specifically, a taking lens is widely used in which the lens group disposed at the rear end of the taking lens along the optical axis constitutes a focusing lens, and focus adjustment is achieved by displacing the focusing lens along the optical axis. In addition, typically, a member that controls the quantity of light, such as a shutter or diaphragm, is provided between the front lens group and the rear lens group or between the rear lens group and the focusing lens.
Conventionally, the digital camera has been made thinner by reducing the spaces between the lens and the shutter or the like as much as possible when collapsing the lens barrel. However, this approach can make the digital camera thinner only to a limited extent.
For providing a thinner digital camera, it has already been contemplated that any of the lens groups of the taking lens is retracted from the optical axis when collapsing the lens barrel. However, there is no proposal concerning which lens group should be retracted or to what position should the lens group be retracted to make the digital camera thinner, or what kind of retracting mechanism should be provided to simply retract the taking lens into a desired position when collapsing the lens barrel and to adequately advance the same lens onto the optical axis when extending the lens barrel.
There has been conventionally known an approach to vary the focal length in which the rear lens group is disposed on the optical axis in the telephoto mode and the rear lens group is displaced from the optical axis in the wide-angle mode (see the patent reference 1). However, this approach is intended only for varying the focal length and does not contribute to making the camera thinner.
In addition, as techniques related to the present invention described later, there have been known shutters using an electrooptic element, such as a liquid crystal shutter using a liquid crystal (see patent references 2 and 3) and a PLZT shutter using a polarizing plate (see patent reference 4).
Patent reference 1: Japanese Patent Laid-Open No. 5- 34769
Patent reference 2: Japanese Patent Laid-Open No. 9-163240
Patent reference 3: Japanese Patent Laid-Open No. 2001-61165
Patent reference 4: Japanese Patent Laid-Open No. 8-304875